1. Field of the Invention
This invention relates to electronic circuits, and more particularly, to measuring integrated circuit (IC) temperature.
2. Description of the Relevant Art
Various processes monitor the temperature of devices for effective control.
These processes may use the substrate temperature of an integrated circuit (IC) for measurement. Manufacturing, automotive and transportation in general, laptops, smart phones, and mobile devices in general, and other fields utilize these processes. Temperature sensors allow ICs to operate under safe thermal conditions to both conserve battery power and prevent damage to on-die transistors.
Examples of temperature sensors include resistance temperature detectors, thermistors, thermocouples, and IC temperature sensors. In contrast to the other types of sensors, the IC temperature sensors do not utilize linearization or cold junction compensation. In addition, the IC temperature sensors generally provide increased noise immunity through higher-level output signals, and some IC temperature sensors provide logic outputs that can interface directly to digital systems.
The IC temperature sensors typically use the property that the difference in forward voltage of a silicon p-n junction is directly proportional to temperature. The base-emitter voltage, VBE, of a bipolar junction transistor (BJT) is one example of a forward voltage of a silicon p-n junction. The temperature measurement of an IC may be performed by measuring the VBE of a BJT at two different current densities at a given location of interest. When a ratio of current densities is set to a given constant value, the measured difference between the two voltage values is proportional to the absolute temperature of the BJT diode. The difference between the two voltage values may be referred to as the delta VBE, or ΔVBE. With accurate knowledge of the values of the two current densities, a calculated temperature value from the measured ΔVBE may be independent of an initial forward voltage, physical size of the junction, leakage, and, to a first order, other junction characteristics, such as a variable non-ideality factor.
A concurrent method for measuring the ΔVBE value utilizes two separate BJT devices and concurrently samples a VBE value for each of the two BJTs. The two separate BJTs may be referred to as thermal BJTs. The concurrent method may generally introduce and suffer from process mismatches between the two separate thermal BJTs, which may in turn affect the overall accuracy of the IC temperature sensor.
A sequential method for measuring the ΔVBE value utilizes a single thermal BJT. A first VBE value is sampled at a first current density followed by sampling a second VBE value at a second current density. An erroneous temperature measurement may occur when an IC's temperature rises sharply in a short time span near a sampling period for the two VBE values. This sharp rise in temperature may occur when a core clock in the IC jumps in frequency, such as when a performance-power state is changed. Alternatively, a sharp rise may occur when one or more portions of the IC transition from a standby state to an enabled state. The error in the temperature measurement may be significant. This error this can lead to a range of unintended consequences, including, but not limited to erratic IC fan spinning, system shutdown, or IC overheating.
In view of the above, efficient methods and systems for measuring IC temperature are desired.